I've used both Dr. Tim's and BioSpiria a few times setting up qt tanks. Between the two, Bio-Spiria was the only one that got close to "instant cycle". So if you are hoping to get fish in right away I would go for BioSpiria.
If you are using it on a tank for coral I recommend you wait a least a week after adding before adding coral - they seem to contain some kind of sticky gel that I presume helps the new bacteria stick to the walls/filters - and I imagine it would also sick on the coral surface and might kill it. This last part is my pure speculation - ymmv.